1. Field
This application relates to an apparatus and method of distilling a liquid such as sea water or, concentrated salt brine, that is capable of separating the dissolved solids into a dry solid by-product and a pure distillate. In the case of sea water the solid by-product is dry salt and the liquid is pure drinking water.
2. Prior Art
Distilling of Sea Water has been, by and large, cost prohibitive, very problematic to keep in operation, and environmentally unfriendly. Both distillation and reverse osmoses systems return concentrated brine along with sometimes, other added chemicals used to de-foam, reduce scale or kill plant growth, to be disposed of, usually back into the ocean. This has caused concern as to the potential damage to the ocean environment that these methods of making drinking water may pose as well as the cost of disposing of this brine effluent. In addition to the environmental concerns that the desalinization process poses, the high costs associated with either distillation or Reverse Osmoses processes have essentially limited or eliminated the wide spread use. When this apparatus and method are embodied as a sea water distillation system, all of these concerns and issues go away. This apparatus can produce drinking water on a large scale, at a price that is competitive with pumping from a ground well, and produces no brine effluent to be disposed of.
Methods for sea water desalination by distillation have been proposed in a number of different technologies. Two major methods are described here as examples:
Distillation Method—Low Efficiency Type
One form of this method involves raising the temperature of sea water at atmospheric pressure above 100.degree C. to produce steam. The steam is then condensed using either ambient air or water as the cooling medium to condense the steam back to pure water. This method has the following advantages:                1. Most bacteria are killed off as the water temperatures are above 65.degree. C.;        2. Systems are easily monitored due to visible boiling taking place;        3. Total Dissolved Solids (TDS) of <20 ppm are left in the distilled water.However this method also has a number of disadvantages including:        1. Very inefficient as heat of vaporization is lost in condensing the distillate.        2. At high temperatures any solids in the sea water will congeal. The congealed solids are deposited on the surface of the heating chamber causing further reduction in efficiency.        
Another form of this method of distilling sea water is to reduce the temperature of the boiling point of water by lowering the pressure in the distillation chamber. This method is favored on ships due to its lower energy consumption. The major drawback with this system is that the distillation temperature is too low to kill bacteria and ultra violet lamp generated ozone is usually needed to kill bacteria in the distilled water. It is also not suitable for large scale applications due to the difficulty of maintaining the distillation chamber at below atmospheric pressures. The above systems use either a boiler arrangement where water is heated and vaporized in the same chamber or an arrangement where water is superheated in a heating chamber and then flashed evaporated in a vaporization chamber. Neither of these approaches have used a water recirculation system to re-circulate the raw water back from the vaporization chamber to the heating chamber for further water reductions.
Distillation Method—High Efficiency Type
High efficiency distillers come in two principle types. The first is the Vapor Compression Distiller and the second is the Multiple Effects Distiller. Both types of distillers recapture the latent heat of vaporization contained in the vapor that is produced. Both of these distillers suffer from the problems of the heating surfaces in the boilers being covered by scale and there by loosing efficiency. When scale builds up, chemicals are added to prevent the build up of scale on the surfaces, or frequent cleaning and down time are the results. Neither type of still can easily be used to produce water and dry salt as this makes the scale problems much worse. Both systems usually return concentrated brine back into the ocean. If chemicals have been added, for any reason, they also are discharged back into the ocean with the brine. The brine, or brine chemical combination, that is discharged into the ocean poses environmental concerns.
Dissolved Salt
For most sea water distillation systems the salt is a great problem and is considered to have no economic value. If the salt could be separated, then it turns out that the salt that is dissolved in ocean water is worth more than the water. Traditional methods of desalinating ocean water do not capture the salt, and the value of the salt is lost. With this apparatus we can separate the salt from the water and sell each product separately. In today's market the value of the salt is enough to pay for the cost of distilling the ocean water with this apparatus. The pure water output is essentially free as though it was being pumped from the ground. Using concentrated brine from any available source as feed stock for this distiller only enhances the profitability of this device.